Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $83.69   12.689%   $94.3094   $94.31   $94.30   $94.30  
  Purchase #2 $126.77   6.281%   $134.7324   $134.73   $134.75   $134.70  
  Purchase #3 $87.60   5.275%   $92.2209   $92.22   $92.20   $92.20  
  Purchase #4 $173.29   5.519%   $182.8539   $182.85   $182.85   $182.90  
  Purchase #5 $211.97   8.655%   $230.316   $230.32   $230.30   $230.30  
  Purchase #6 $248.38   6.145%   $263.643   $263.64   $263.65   $263.60  
  Purchase #7 $250.71   13.372%   $284.2349   $284.23   $284.25   $284.20  
  7 purchase totals = $1,182.41       $1,282.3105   $1,282.30   $1,282.30   $1,282.20